Limit control



w. A. RAY

LIMIT CONTBOL Jan. 10, 1939.

Filed Sept. 9, 1935 F'IE E INVENTOR. 67 W/'///'a/77 4. Fay L- v @w 1. 44

ATTORNEY.

FIE -Q= Patented Jan. 10, 1939 UNITED STATES PATENT OFFICE LIMIT CONTROL California Application September 9, 1935, Serial No. 39,728

Claims. (01. ass-ca) This invention relates to a limit control device, particularly one adapted to the control of a domestic heating furnace and the like.

In the operation of a domestic heating furnace, 5 for example, it is desirable that the control device be capable of procuring a throttling action upon such means as the heat supply means. Thus, if a room thermostat calls for a temperature of 70 F. and the temperature in the room is actually 50 F. there is no objection whatsoever to the heat supply means for the furnace operating at full capacity. However, if the temperature in the room is 6?", full capacity oper-' ation of the heat supply means will result in inefficient operation and an overrunning of the temperature of 70. Theoretically the most desirable operation condition would be that in which the heat supply means operated in proportion to the difierential existing between the desired temperature and the actual temperature. Such operation requires a fluttering action, a throttling down of the amount of heat supply as the differential decreases so that the heat supply rate diminishes in proportion as the differential between the actual and the desired temperature. In accordance with the present 'invention this manner of operation is attained by creating a false thermostat temperature and' by utilizing this false temperature to control operation of the heat supply means. In actual practice the invention can be considered as comprising two units, a control unit for the fuel supply and-a limit control device operating upon the temperature of the room. The first unit, for example, can include a valve controlling the source of heat supply. This can be steam, or a fuel supply to a burner. The valve is adapted to be opened and closed for example by a reversible motor operating through a gear train. The rate of opening or closing movement of the valve is usually quite slow and a goodly time interval, such as ten minutes, is contemplated within which the motor will run to move the valve to either its full open or full closed position from a full closed or a full open position. Operation of the motor is under'controlof the room thermostat. Now if this thermostat is ina room at a temperature of say 50 F. and is set to maintain a temperature of 70 F. it will close the circuit to the motor and opening movement of the heat supply valve will start. At the same time, in accord ance with this invention, the thermostat is heated by a heat supply means directly associated with the thermostat. Since this heat supply means is provided to have a certain rate of heating, and

since a considerable differential exists between the actual room temperature and that which is desired, some time will elapse before the thermostat attains that temperature at which it will shut off operation of the motor opening the heat I supply valve. During this time the heat supply at the maximum rate., When the thermostat f does cut off, opening movement of the heat supply valve, the valve remains open. However, the heating of the thermostat is under control of another device which is associated with the opening of the heat supply valve. In one instance, to be hereinafter set forth, a strip of bimetal is likewise heated and is included in a unit controlling the heating of the thermostat. This strip of bimetal being likewise heated, results in a breaking of the circuit to the heater on'the thermostat.

When the room temperature begins to raise, the thermostat of course due' to its artificial temperature loading from the associated heating means reverses operation of the motor and starts a slow closing movement of the fuel supply valve. However, the aforementioned bimetal strip is effective to open the heating circuit of the thermostat and the thermostat therefore is notheated continuously with the result that it works back and forth. In actual operation, the false temperature loading decreases as the temperature of the room rises and as it approaches the value for which the thermostat is set it decreases almost entirely until the thermostat finally shuts off.

The device that has been described makes possible the use of remote control of a heat supply means, for example, to the end that a throttling action can be'secured on the heat supply means. In its simplest form, the limit control device described can be made to function at a considerable distance from the heat supply means with only four wires. The advantage of such a structure is obvious and it is therefore in general the broad object of the present device to provide an improved limit control device enabling control to be maintained and an operation to be secured which is in relation to the difference existing be tween the set of existing conditions and the set of desired conditions. The device is of course applicable to pressure control as well as temperature control and the previous discussion of the thermostat can be substituted for by a pressure responsive development to the end that a desired pressure can be maintained.

The invention includes other objects and features of advantage, some of which, together withthe foregoing, will appear hereinafter wherein I have disclosed the preferred form of my inven tion.

- In the drawing accompanying and forming a part hereof Figures 1, 2 and 3 are diagrammatic representations of apparatus and circuits for practicing the present invention while Figure 4 is a fragmentary plan view of a control device.

In accordance with this invention I provide means for controlling the operationof the device, in this instance a furnace 6 being chosen as illustrative. A burner 1 cooperates with and supplies heat to the furnace 5. Fuel I is supplied to the furnace 1 through line 8 and the flow thereof is through a valve 9, the heat supply control valve. This valve includes anvalve seat ii and a cooperative valve member i carried upon a valve stem l3. The valve stem is raised and lowered by a suitable motor ll. Thismotor can be either electrically or thermally operated and is adapted to move the valve stem positively in two directions so that the valve member l2 moves toward and away from the seat il. Suitable electrical and thermal motors of this type are well known and need not be further discussed here except to say that I have chosen for purposes of illustration an electric motor in which the motor can be rotated in either direction to raise or lower the valve stem I3 slowly through a suitable gear train. The valve stem l3 includes an arm It carrying a contact Hi. This contact cooperates with a contact 96 carried upon an insulated extension ll of a bimetal strip 58. Bimetal strip i8 is supported from a fixed support I9 by a like bimetal strip 2i. The two bimetal strips are so placed and connected that ambient temperature is compensated and need not be considered. The heating element 22 is connected to the contact l6 and to the bimetal strip i8 with which it is in good thermal contact so that, upon current passage through the heating element, heat is generated therein and the bimetal strip is in turn heated with the result that a flexing in a clockwise direction in Figure 1 occurs. Contacts l5 and I6 and the heating element 22 are included in a circuit with a secondary 23 of a step down transformer having a. primary 24'. Also included in this circuit is a heating element 26 carried upon a bimetal strip 21. An insulated strip 28 attached to the bimetal strip 21 carries a movable contact 29 which cooperates with flxed contacts 3| and 32 positioned on opposite sides of contact 29. A power source typified by lines 33 and 34 is connected respectively to the contact 29 and to the motor l4. Current passage to the motor from line 3 is through lines 36 and 31,-these lines being respectively connected to difierentwindings, for example, in the motor to secure a diflerence in the direction of the rotation thereof so that the valve stem l3 can be slowly raised or lowered positively. In operation, the bimetal strip 21 is subject to some temperature condition, for example that in a room. If the temperature drops too low the bimetal flexes in a clockwise direction in Figure l and contacts 32. Current then passes to the motor 14 and the valve stem I3 is slowly raised bringing the contact l5 into contact with the contact l6. This results in a means.

rection, while bimetal strip 21 flexes in a counterclockwise direction as shown in Figure 1. Contacts i5 and it remain in engagement, however, due to continued movement of contact 15, while contact 29 is carried away from contact 32 breaking the circuit to the motor and leaving the valve in an open position. This does not at once discontinue the heating of the bimetal strip 21, however, and the bimetal strip 21 will continue to fiex-until it engages contact 3i. This results in the motor moving valve stem i3 downwardly and, at the same time opening contacts I5 and i6 and discontinuing heating of both heating coils 22 and 26. Subsequently, the bimetal strip I8 will cool and, depending upon the relation of its temperature and the position of contact I5, it may or may not again engage the contacts l5 and it to cause fluid flow to the burner 1.

The actual operation of the structure disclosed, in. relation of the bimetal strips l8 and 21 and their associated heating coils is such that the bimetal strip 21 operates under a false temperaenable a fluttering action of the heat supply control means typified by the valve 9. It is to be remarked that the control efiected over the heat supply control means is a remote one for direct mechanical connection need not be provided between the bimetal strip, or other control means, and the valve 9. As a matter of fact, the system can be operated with as ,few as four wires and these can extend for any desired distance so that the heat supply control means can be remotely located with respect to the thermostatic controlling its operation.

In operation, the bimetal strip 21 will secure a supply of heat at a rate in proportion to the necessity demand or, in other words, in proportion to the differential existing between a desired condition and the actual condition. For example, if a temperature of 70 F., is desired and a temperature of 50 F. exists, depending upon the setting of the particular apparatus, it is the function of the bimetal strip 21 to continue initially the full rate operation of the heat supply control Thus the heater 26 on the bimetal strip will have to supply a goodly quantity of heat, in view of the 20 difierential existing before the bimetal strip will flex and carry contact 29 away from contact 32. During this time the motor has been slowly raising the valve stem i3 and the heat supply control is nearly wide open. When the contact 29 is separated from the contact 32 operation of the heat supply is not cut off but continues at the rate at which the valve determines. It is only'upon continued heating that heater 22 carries contact l6 away from contact l5. This shuts off the heat to both heaters and bimetal strip 21 thereupon assumes its condition in relation to the temperature which exists in its locality. If this temperature is low it can contact 32 to result in a further opening of the heat supply control means.

The bimetal strip I8 is or course independent 01' the ambient temperature and it therefore will flutter on and 05 to supply'heat to the heater 26 on bimetal strip 21. As the temperature differential decreases between the actual temperature and that desired, it temperature is utilized as the controlling condition, the false temperature load on the bimetal strip 21 will of course decrease as the difierential decreases for engagement of contact 29 with contact 3| will result in the lowering of the valve stem.i3 and a repositioning of contact l5. This requires that ture loading. The purpose of this loading is to 2,143,210 3 the bimetal strip l8 cool more each time with the open position, resistance means, a contact moved result that the heatings o! bimetal strip 21 beby said member over said resistance means, a

come fewer and fewer so that it assumes the bimetal strip including a metal fin, said strip position more nearly identical with that of the controlling operation of said motor, a core havroom temperature. Since contact I5 is being ing opposite pole pieces, a coil and a shading coil lowered it will also require less heating of bimetal cooperating with said fin to provide a shaded strip l8 to separate contacts l5 and IS with the pole motor, and means connecting said coil and result that the quantity of heat supply to the bisaid resistance means to a source of current. metal strip 21 is decreased. In this way a throt- In combination, a thermostat including tling action of the heat control supply means is b e l str p a ta fi a d b said strip and secured and in operation 01. the furnace is cocccpcmting With a Shaded D 00m to Provide ordinated with the degree of demand. shaded P motor f moving s d t p- In Figure 2 I have shown another modification In ,ccmblnaticn, a thermostat including a in which the valve stem l3 carries an arm 4| to metal Strip, a metal fin carried y Said Strip and which is afiixed a contact 42 which slides over a cooperating With a Shaded D core to Provide a rheostat 43. Contact 42 and rheostat 43 are con- Shaded D Inciicl for moving Said p, a o nected in series with a source of direct current on Said core, and means for energizing s d 001 and with a solenoid 44. This solenoid includes Selectively and to f re t xtents.

a core 46 of the floating type supported by bell In combination. D y condition 00 crank 41. The bell crank is also connected by a t means, means for controlling a d p ma y link 48 to a movable contact arm 49 which moves means including. a thermostat including a b between contacts 3| and 32 to client the same metal p. a metal fin carried y Said Strip and control as is secured by the bimetal strip 21 and cooperating w t a s d d p core to p v d its contact 29. a shaded pole motor for moving said strip, a coil In Figure 3 is disclosed a preferred form of On Said core, n means for energizing id c l control device for the motor and valve, In thi selectively and to difierent extents dependent form bimetal strip 21 carries a copper fin 6| exupon positioning of said pr mary control means. tending between pole pieces 62 and 63 of core 64. In combination, a n r l d vic s a valve. A shading coil 66 is carried by pole 63 while a said device including an element movable over winding 61 is connected to a source of A. C. and a pa h, a r s tan a c ntact m va l by said resistance 43. The copper fin cooperate with th element over said resistance during movement of core 64 to provide a shaded pole motor, the bi-. a d element Over d P a Operable metal taking up instantaneously a position n in opposite directions to move said element, a bisponding to that determined by resistance 43 and m a Strip, contacts cooperating with Said t p Contact 42. This is a very simple, inexpensive to control operation of said motor, a field coil and yet rugged and responsive device operable on in a circuit with said contact and said resistance, A. C. without hum. said resistance and contact controlling the ef- I claim: fective field strength of said coil, and a metal fin 1. In combination, a valve, means for moving member carried by Said Strip and mov ble y said valve including a slow operating motor and the field created by said field coil for moving said a member movable over a path having one exstrip. treme corresponding to a valve closed position WILLIAM A. RAY. and another extreme corresponding to a valve 

